Reservation multiple access

ABSTRACT

A mobile station accesses a base station by randomly selecting a first reverse link common control channel from a set of random access channels. The mobile station transmits a request portion of an access probe over the first reverse link common control channel. The request portion is subject to collision with other signals. The request portion comprises a hash identification which is derived from a uniquely identifying number using a hash function. The hash identification quasi-uniquely identifies the mobile station. The mobile station receives a channel assignment message from the base station designating the hash identification and a reserved access channel. The reserved access channel provides communication with a low probability of contention. The mobile station transmits a message portion of the access probe over the reserved access channel.

RELATED APPLICATIONS

This patent application is a continuation part of and claims priorityunder 35 U.S.C. 120 to U.S. patent application entitled, “ReservationMultiple Access”, Ser. No.: 09/173,572, which was filed on Oct. 15, 1998now U.S. Pat. No. 6,256,301.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The invention relates generally to wireless communications. Moreparticularly, the invention relates to multiple access in a wirelesscommunication system.

II. Description of the Related Art

In a typical wireless communication system, a plurality of mobilestations communicate through a common base station. Because the basestation has finite resources available, the mobile stations compete foraccess to the base station resources. FIG. 1 is a block diagram showinga typical modern wireless communication system 10. The system iscomprised of a series of base stations 14. A set of mobile stations 12communicate with the base stations 14. The mobile stations 12communicate with the base stations 14 over a forward link channel 18 anda reverse link channel 20. As used herein, the term “channel” refers toboth a single communication link between the base station and a specificmobile station as well as a grouping of communication links, typicallyhaving a common function. FIG. 1 shows a variety of types of mobilestations. For example, FIG. 1 shows a hand-held portable telephone, avehicle mounted mobile telephone and a fixed location wireless localloop telephone. Such systems offer voice and data services. Other modemcommunication systems operate over wireless satellite links rather thenthrough terrestrial base stations.

An industry standard for a wireless system using code division multipleaccess (CDMA) is set forth in the TIA/EIA Interim Standard entitled“Mobile Station—Base Station Compatibility Standard for Dual-ModeWideband Spread Spectrum Cellular System”, TIA/EIA/IS-95, and itsprogeny (collectively referred to here in as IS-95), the contents ofwhich are also incorporated herein by reference. Among other channels,IS-95 defines a reverse link random access channel which is used by themobile stations to communicate with a base station. The access channelis used for short signaling message exchanges such as call originations,responses to pages and registrations. For example, for prolongedbi-directional communications, a dedicated forward link and reverse linktraffic channel pair are established between the mobile station and thebase station. The access channel can be used to transfer informationfrom the mobile station to the base station before the traffic channelis established in order to facilitate establishment.

The access channel defined by IS-95 is a random access channel meaningthat a mobile station randomly chooses a portion of the access channelresources over which to transmit an access probe. Due to the randomnature of the access channel, there is no guarantee that only a singlemobile station will attempt access on the chosen portion. Therefore,when an access probe is sent, it may fail to be received by the basestation for one of several reasons. It may fail because the power levelreceived at the base station is too low compared to the currentinterference levels. It may fail because another mobile station attemptsto use the same portion of the access channel resources at the same timecausing a collision. In any case, when the access probe is not receivedat the base station, the mobile station randomly selects another portionof the access channel resources and attempts access to the system,perhaps using a higher signal level. In order to avoid a series oflockstep failures between two mobile station after an initial collision,the retransmission process is also randomized.

In order to select a portion of the access channel resources, accordingto IS-95, the mobile station randomly selects one of a set of one ormore access channels defined by CDMA techniques. Once an access channelis selected, the mobile station is constrained to begin transmission ofthe access probe at one of a set of re-occurring slot boundaries. Themobile station randomly selects a slot boundary and begins transmission.Such operation is referred to as slotted aloha operation and is wellknown in the art.

One key aspect of a random access system is load control. Load controlis used to statistically control the rate at which access probes arereceived at the base station. Load control in a slotted aloha system isimportant because as the number of access attempts increases, the numberof collisions also increases. As the loading further increases, thenumber of successful access attempts actually begins to fall due to thesystem resources being consumed with collisions. Therefore, in a slottedaloha system, it is advantageous to keep system loading at less than 18%of the fully loaded capacity, otherwise unstable behavior can result.

Loading is also a function of the amount of interference in the system.The available capacity of a system decreases as the interferenceincreases. As the load on the random access channel increases, it maycause significant interference to other channels in the system such asthe traffic channels. According to IS-95, loading on the access channelis controlled by the insertion of random delay (called access probeback-off) between a failed access attempt and a follow up attempt.However, IS-95 lacks any mechanism for quickly enabling and disablingaccess to the access channel in order to control loading.

According to IS-95, when a mobile station sends an access probe, ittransmits a uniquely identifying number such as the electronic serialnumber (ESN) of the mobile station along with other information in apreamble. In addition, the access probe comprises a message whichspecifies the purpose of the probe or carries user data. For example,the message may designate a telephone number for use in a callorigination. An access probe is typically between 80 and 150milliseconds (msec) in duration.

According to IS-95, the mobile station initially transmits the accessprobe at a first level. If the base station does not respond with anacknowledgment after a predetermined amount of time, the mobile stationcontinues to repeat the access probe at increasingly higher powerlevels.

This method of access does not yield a very efficient use of systemresources. First, the access probe is fairly lengthy and the mobilestation continues to transmit the entire access probe even if the basestation is unable to receive the access probe, thus, spewing un-usefulenergy into the system, wastefully expending mobile station resourcesand reducing system capacity. According to IS-95, once the mobilestation has begun to transmit, no power control mechanism exists bywhich the base station can increase or decrease the transmit power. Ifthe reverse link is subjected to a deep fade, the transmission may failand the mobile station retransmits the message at a higher power levelwhich may not be necessary in the absence of the fade. The base stationhas no means to request more power during the deep fade nor to request areduction in power during the subsequent retransmission. In addition toconsuming significant system resources, the access method according toIS-95 can stretch to cover a significant amount of time adding delay tothe system. According to IS-95, data is transmitted over the accesschannel at only one data rate regardless of the amount of data or thequality of the connection between the mobile station and the basestation.

Thus, there has been a need in the art to develop a multiple accesssystem which introduces less delay and makes more efficient use of theavailable system resources.

SUMMARY OF THE INVENTION

Reservation multiple access (RsMA) is used to provide multiple access toa plurality of mobile stations. The access probes used to access thesystem are divided into two different portions: a request portion and amessage portion. The request portion comprises a number which“quasi-uniquely” identifies the mobile station. For example, a hashidentification can be derived from a longer number which uniquelyidentifies the mobile station using a hash function. The request portionalso comprises a preamble to facilitate detection. The length of therequest portion is small in comparison to the length of the messageportion.

The request portion is sent over a random access channel. For example,in one embodiment, the request portion is transmitted over slotted alohachannel in which the slot boundaries follow closely after one anothersuch as on the order of the length of several request portions.

If the request portion is properly detected by the base station and ifresources are available, the base station assigns a reserved accesschannel using a channel assignment message. The channel assignmentmessage comprises the hash identification. The mobile station sends themessage portion over the reserved access channel. The reserved accesschannel provides communication with a low probability of contention. Inone embodiment, the message portion can comprise a request for a trafficchannel or other system administration message or it may contain adatagram of user information. In one embodiment, the message portion cantake on one of a set of variable data rates.

In another embodiment, a forward link channel sends power controlinformation to the mobile station while it is transmitting over thereserved access channel. In yet another embodiment, the channelassignment messages, the power control information, or both, are sentfrom a plurality of sectors, base stations or both.

In one embodiment, a base station send can send a wait message to aspecific mobile station or to a class of mobile stations over theforward link channel assignment channel which also carries the channelassignment messages. The wait message delays subsequent access attemptsby the subject mobile stations. In another embodiment, a wait messagecan be used to quickly disable access to the system in order to controlloading.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram showing a typical modern wirelesscommunication system.

FIGS. 2A and 2B are flow charts showing mobile station operation inRsMA.

FIG. 3 is a representational diagram showing a series of channels in aRsMA system.

FIG. 4 is a representational diagram showing an exemplifying datastructure for the forward power control common channel.

FIG. 5 is graph illustrating mobile station transmission power in aclosed loop system.

FIG. 6 is a representational diagram showing the coverage area sectorsof a multisectored base station.

FIG. 7 is a block diagram of the multisectored base station.

FIG. 8 is a block diagram of an exemplifying mobile stationarchitecture.

DETAILED DESCRIPTION OF THE INVENTION

In order to overcome the limitations of the prior art, the inventionuses a reservation multiple access (RsMA) format to facilitate randomaccess to the system. In order to increase efficiencies, the accessmessage is divided into two different portions: a request portion and amessage portion. The request portion is sent over a random accesschannel. In response, a reserved access channel is assigned. The messageportion is sent over the reserved access channel. Through the use of areserved access channel, in one embodiment, closed loop power control isapplied to the message portion of the access probe. Together with otherfeatures, the invention lends efficiencies to the access process.

The invention is best understood by way of example. FIGS. 2A and 2B areflow charts exemplifying mobile station operation in a RsMA systemaccording to the invention. FIG. 3 is a representational diagram showinga series of channels and messages in a RsMA system which can be used tofacilitate an understanding of FIG. 2.

Referring to FIG. 2A, flow begins in start block 100. In block 102, thesequence number and probe number are set to 0. In block 104, the mobilestation randomly selects a forward link channel assignment channel(F-CACH) from a set of forward link channel assignment channelssupported by the system. For example, the mobile station selects then-th forward link channel assignment channel such as F-CACH(n) 200 shownin FIG. 3. In one embodiment, the number of forward link channelassignment channels is programmable and can be reduced to 1 or even 0 inorder to reduce the number of successful accesses.

In block 106, the mobile station estimates the signal quality of thepilot signal received from the corresponding base station. For example,the mobile station may estimate the ratio of the energy in the carrierto the noise power density (E_(c)/I_(o)) at which the pilot signal isreceived. Block 108 determines whether the pilot signal quality exceedsa predetermined threshold. If not, the mobile station assumes that theforward link channel has faded and flow continues back to block 106until the signal quality improves. Due to the rapid fading nature of theterrestrial channel, adverse fading conditions typically correctthemselves quite rapidly. By avoiding transmission during a deep fade,the mobile station can increase the likelihood that it will receive abase station response on the F-CACH as described in more detailed below.Blocks 106 and 108 are optional and some embodiments may not containthis feature.

If it is determined in block 108 that the signal quality of the pilotsignal exceeds the threshold, flow moves to block 110 wherein the mobilestation randomly selects a reverse link common control channel (R-CCCH)corresponding to the selected R-CCCH. For example, the mobile stationselects the c-th reverse link common control channel, such as R-CCCH(c)202 shown in FIG. 3. In one embodiment, the F-CACH is associated with aplurality of R-CCCH. In block 112, the mobile station initializes thetransmit power to an initial power level (IP). In one embodiment, thevalue of IP is determined based upon the signal quality of the pilotsignal as well as other factors. In another embodiment, the value of IPis a fixed or programmable value. Flow continues through off pageconnector 114 to off page connect 116 of FIG. 2B.

In block 118, the mobile station transmits a request portion of anaccess probe comprising a preamble and hash ID over the R-CCCH(c) 202,as shown by the request message 210. The hash ID is derived frominformation that is unique to the transmitting mobile station. Accordingto one of a plurality of well known techniques, the hash value isgenerated by a hash function that maps an input number comprising alarge number of bits into an output number that is shorter. For example,in one embodiment of the invention, the input information for the hashfunction comprises the electronic serial number (ESN) of the mobilestation which is, according to IS-95, a 32 bit number assigned by themobile station manufacture which uniquely identifies the mobile stationequipment. Using 32 bits, over four billion mobile stations can beassigned a unique ESN. The output of the hash function is, for example,a 12 bit number defining 4096 different “quasi-unique” hash ID values.Although not unique, the length of the hash ID is sufficient to make itextremely unlikely that more than one mobile station operating withinthe coverage area of a base station will generate the same hash ID andtransmit the request portion of an access probe at the same time. Theuse of this hash ID allows less information to be transmitted comparedto IS-95, while still distinguishing that mobile station from all othersin the area in the vast majority of cases. If a collision occurs betweentwo or more mobile station using the same hash ID at the same time, someor all of the access attempts may fail. In such a case, the unsuccessfulrequest portion is retransmitted again and the random back-off periodsreduces the risk of a subsequent collision.

Eventually, during the course of the access, the mobile station must beuniquely identified to the base station. However, such uniqueidentification is not necessary in order to proceed with system accessat this point. The use of a hash ID significantly reduces the amount ofdata which is transmitted in the request portion of the access probe.According to the invention, unique identification of the mobile stationis accomplished within the message portion of the access probe ratherthan in the request portion.

In block 120, the mobile station monitors the F-CACH(n) 200 to determinewhether the access probe is successfully decoded by the base station.For example, in FIG. 3, in one scenario, the base station responds bytransmission of a responsive message 212. The responsive messagecomprises the hash ID of the mobile station to which it is directed. Theresponsive message also comprises a cyclic redundancy check (CRC) valueor other error detection mechanism. In one embodiment, the F-CACH(n) 200is associated with a number of R-CCCH(c) and can carry messages intendedfor a number of different mobile stations, each of which includes a CRCvalue. In block 122, the mobile station monitors responsive messagescarried on the F-CACH(n) and determines whether a failure is detected byreliance on the CRC. If a failure is detected, flow continues in block126 as explained below. In one embodiment, the base station retransmitsa repeat responsive message 212′ if no response from the mobile stationis detected. In FIG. 3, the response message is repeated D2 secondsafter the end of the initial transmission such that the mobile stationtimer D1 does not expire until the end of the repeated response message212′. In one embodiment, the mobile station soft combines energy from tooriginal response message 212 and the repeat response message 212′ toimprove performance according to well known techniques.

If no failure is detected in block 122, the process moves to block 124and determines whether the specified hash ID transmitted in theresponsive message 212 carried on the F-CACH(n) 200 matches the hash IDtransmitted by the mobile station. If the hash ID does not match or if afailure was decoded in block 122, flow continues to block 126. Block 126determines whether the D1 timer has expired. The D1 is reset when therequest portion of the access probe is transmitted and accumulates timeuntil it has timed out. For example, in FIG. 3, the period of the D1timer is indicated by the double arrow line labeled D1, beginning fromthe end of the request portion 210 of the access probe. If the D1 timerhas not expired, the mobile station continues to monitor the F-CACH(n)200 beginning in block 120.

If the hash ID matches, flow continues from block 124 to block 146.Block 146 determines whether the responsive message 212 is a waitmessage. For example, the base station may send a wait message whichdirects the mobile station to attempt access again after the passage ofsome amount of time. In this way, the base station can control the basestation loading caused by the mobile stations using these reverse linkchannels. By setting the wait time to infinity, the system has amechanism for quickly disabling access to the access channel in order tocontrol loading. If the message is a wait message, flow continuesthrough off page connector 148 to off page connector 158 of FIG. 2A. Inblock 160, the mobile station generates a pseudo random number PN(b) tobe used for a back-off timer. In block 162, the mobile station waitsPN(b) slot times before re-entering flow to attempt another access. Inone embodiment, the wait message simply directs the mobile station toenter the routine which chooses the back-off period. In anotherembodiment, the base station can direct the mobile station to wait anadditional amount on top of the wait specified by the randomly chosennumber. In yet another embodiment, the base station can specify a factorby which the back-off period is multiplied in order to change the waitperiod.

Returning again to FIG. 2B, if no wait message is received in block 146,flow continues to block 150. Block 150 determines whether a channelassignment message is received. If no channel assignment message isreceived, flow continues to block 152 where access failure is declaredand the mobile station enters a system determination state. In otherembodiments, other types of responsive messages are included in thesystem and are detected before a failure is declared.

If a channel assignment message is detected in block 150, flow continuesto block 154. The channel assignment message specifies a reverse link,reserved access channel (R-RACH) for use by the mobile station, such asR-RACH₁₃ 1 204 shown in FIG. 3. The reserved channel is not subject tocontentions with high probability because the likelihood of two or moremobile stations accessing the system with the same has ID is very small.In addition, in one embodiment, the reserved channel is associated witha forward link power control channel (F-PCCH), such as F-PCCH_1 206shown in FIG. 3, which provides closed loop power control for the mobilestation as explained below. In one embodiment, based upon the assignmentof the R-RACH₁₃ 1, the mobile station can determine the associatedF-PCCH. In another embodiment, the channel assignment message specifiesboth a R-RACH and a F-PCCH.

In one embodiment, the channel assignment message can specify a waitperiod. In this embodiment, the base station determines that a certainR-RACH which is currently in use will be available at some time in thefuture. It may make this determination based upon the known length of amessage already in progress or based upon a known maximum length formessages. In essence, the time delayed channel assignment message tellsthe mobile station to begin transmission on the specified R-RACH after apredetermined number of frames have passed. This type of operation hasthe advantage of freeing the R-CCCH for use by other mobile stations,thus, decreasing the number of collisions and increasing the overallefficiency of the system.

In block 154, the mobile station transmits a message portion 214 of theaccess probe on the assigned reverse reserved access channel R-RACH₁₃ 1204 and receives power control commands 216 on the associated F-PCCH_1206 as explained more fully below. The message portion can comprise aresponse to a page, an original request for a traffic channel, adatagram bearing user information in a digital data system, or othertype of message. In block 156, the mobile station has completed theaccess attempt and the access routine enters an idle state.

Returning again to block 126, if the D1 timer expires before a matchinghash ID is detected in a correctly received response message, flowcontinues to block 128. In block 128, the probe count is incremented.Block 130 determines whether the probe count is less than a threshold.If so, the maximum number of access probes have not been sent and flowcontinues to block 144 in which mobile station generates a random numberPN(p) for the back-off period. In block 142, the flow waits theprescribed number of time slots designated by PN(b). In block 140, themobile station increases its transmit power and flow continues back toblock 118 where the access probe is transmitted at the higher powerlevel over the R-CCCH(c).

If it is determined in block 130 that the maximum number of accessprobes have already been sent over the previously chosen R-CCCH, flowcontinues from block 130 to block 132. In block 132, the sequence numberis incremented. Block 134 determines whether the sequence number is lessthan a prescribe threshold. If so flow continues through off pageconnector 138 back to FIG. 2A where, after a random delay, the mobilestation randomly selects a new F-CACH and R-CCCH pair over which toattempt access to the system. If it is determined in block 134 that thesequence number is greater than or equal to the maximum sequence number,flow continues from block 134 to block 136 in which access failure isdeclared and the mobile station enters a system determination state.

The operation just described has a number of advantages in relation tothe access scheme defined in IS-95. The request portion of the accessprobe is transmitted over a slotted aloha channel in a similar manner asthe access probe in IS-95. However, according to IS-95, the mobilestation transmits an entire access probe comprising a lengthy ESN andmessage which may have a duration as long as 520 msec. According toIS-95, the mobile station then monitors a paging channel for as much as1360 msec for a traffic channel assignment message from the basestation. If the traffic channel assignment message is not received, themobile station sends the entire access probe again after insertion of aback-off period which can be as long as 8320 msec. Thus, in the event ofa failure, as much as 9680 msec passes before the mobile stationretransmits the entire access probe, typically at a higher power levelthan before, spewing even more energy into the system.

Thus, according to IS-95, typically 150 msec or more of energy istransmitted over the reverse link access channel whether or not the basestation can detect the signal. In this way, significant energy is expendon futile access attempts lowering the efficiency of the mobile stationpower consumption and creating useless interference to the system. Inaddition, this type of operation introduces a significant delay in theevent of an initial failure. The invention overcomes these limitations.

Under IS-95, the base station does not establish a forward linkconnection to the mobile station until the entire access probe has beenreceived. Therefore, the base station has no way of transferring powercontrol information to the mobile station during the transmission of thelengthy access probe. Without any power control, both the likelihood ofexcessive power generation (due to a transmission power level which istoo high) and the likelihood of repeat transmission (due to atransmission power level which is too low) are increased, thus,increasing the level of interference to the system. In one embodiment,the invention also overcomes this limitation by providing closed looppower control for the message portion of the access probe.

According to well known, acquisition techniques, detection of the mobilestation signal by the base station requires only a very small fractionof energy transmitted in the prior art access probe. Therefore, incontrast, the present invention uses of the request portion of theaccess probe in order to facilitate detection of the mobile stationsignal by the base station. The request portion of the access probe issignificantly shorter than the access probe in IS-95. For example, inone embodiment, the entire request portion can be transmitted in 2.5msec. Typically, the ratio of the duration of the request portion to theduration of the message portion is very small such as on the order of0.01.

After transmission of the brief request portion, the mobile stationceases to transmit. If the base station receives the request, itresponds with the brief channel assignment message. Again, the messagemay be relatively short as it specifies the hash ID rather than theentire ESN. For example, in one embodiment, the reserved access channelassignment message is 3.75 msec in length. In this way, transmission ofthe reserved access channel assignment message does not consumesignificant system resources. And, in this way, the mobile station isinformed rather quickly as to whether the base station was able todetect its signal. For example, in FIG. 3, if the response message 212is a channel assignment message for the mobile station, the mobilestation is aware that the base station detected its signal approximately5 msec after the end of the transmission of the request portion. Thisentire transaction can take place in about {fraction (1/20)} of the timenecessary to just transmit an access probe according to IS-95.

Due to the short duration of the request portion of the access probe,the slot boundaries upon which the mobile station is permitted to begintransmission according to slotted aloha operation can follow closely oneafter another. In this way, the number of possible transmission times isincreased which reduces the probability of collision and allows for moremobile stations to be supported by the random access channel. Forexample, according to IS-95, the slot boundaries occur at a rate of 1.92to 12.5 boundaries per second. In one embodiment, the slot boundaries ofthe invention occur at a rate on the order of 800 boundaries per second.If two mobile stations transmit during the same slot boundary but thebase station is able to detect one or both of the requests due todiversity such as time diversity due to path delays, the base stationmay assign each contending mobile station to a different R-RACH byreference to the hash ID, thus allowing the system to capture contendingmobile stations in some situations.

If a failure does occur, the mobile station is aware of the failurewithin the period D1 which is, in one embodiment, on the order of 40 to60 msec. The mobile station can send a follow up request portion on oneof the rapidly occurring slot boundaries which follows, thus reducingthe delay introduced by a failure. In addition, due to the brevity ofthe request portion, the amount of energy spewed uselessly into thesystem is greatly reduced in comparison with IS-95.

Once the mobile station is assigned a reserved access channel, thetraffic channel assignment process can proceed in much the same manneras IS-95. In addition to the message portion which specifies theresources requested by the mobile station, the mobile station alsotransmits a short preamble in the message portion of the access probe sothat the base station can detect the signal and perform coherentdemodulation. In one embodiment, the preamble in the message portion isabout 1.25 msec long.

One significant advantage of the use of the reserved multiple accessscheme is that a forward link connection from the base station to themobile station is readily established in parallel with the reverse linkreserved multiple access channel. In contrast, according to operationunder IS-95, the base station does not fully detect the mobile stationuntil the entire access probe has been received and the mobile stationdoes not begin to monitor for forward link signals until the entireaccess probe has been transmitted. However, in accordance with theinvention, the base station is aware of the mobile station aftertransmission of the request portion. The assignment of the R-RACH allowsa parallel forward link connection to the mobile station to be readilyestablished. The base station can monitor the R-RACH assigned to themobile station in order to quickly detect any transmission made by themobile station.

As noted above, in one embodiment, the system uses a parallel forwardlink channel to implement closed loop power control of the mobilestation transmission power during transmission of the message portion ofthe access probe. Closed loop power control refers to control of themobile station transmission power by the base station. The base stationdetermines the proper transmission level based upon the actual operatingconditions at the base station. As shown in FIG. 3, in one embodiment, asingle F-PCCH is associated with a plurality of R-RACH's. The powercontrol commands for multiple mobile stations are time multiplexed ontothe channel in a predetermined manner such that when a mobile station isassigned to a R-RACH, it can determine which information on the F-PCCHcorresponds to its own transmission. In an alternative embodiment, thepower control packets can be interleaved with data on a separate channelsuch as in a similar manner to the traffic channel operation accordingto IS-95. In one embodiment, the power control rate is a programmable.For example, power control commands may be passed to the mobile stationat 0, 200, 400 or 800 commands/second. The power control rate may dependon the length of the message as well as other factors such as systemloading. A rate of 0 commands/second may be used if the message is soshort that the power control won't take effect until after the messagehas ended.

Referring now to FIG. 4, an exemplifying structure of a stream of powercontrol information packets 250 is shown. Each power control informationpacket 250 is capable of carrying N power control commands 252A-252N. Inthis way, N different R-RACH can be associated with a single F-PCCH. Inthe embodiment shown in FIG. 4, each power control command 252 in thepower control information packet 250 maps to a single R-RACH and is usedto control the output power of the mobile station communicating overthat R-RACH. Thus, the power control command 252A controls the outputpower level of the mobile station transmitting on R-RACH₁₃ 1, the powercontrol command 252B controls the output power of the mobile stationtransmitting on R-RACH_2, and so on. As noted above, in one embodiment,the system allows for variable rate power control, such that some of thepower control information packets 250 can comprise more than one commandintended for a single mobile station or the F-PCCH can control more thanN R-RACH by time multiplexing power control commands in successive powercontrol information packets. In such a case, the mapping of the powercontrol information packets to the associated R-RACH becomes lessuniform but operates under the same principles.

In one embodiment, the power control commands are a single bit in lengthand the mobile station either raises or lowers its transmit power inaccordance with the single bit value in a similar manner as trafficchannel in IS-95. When a mobile station begins to transmit on aparticular R-RACH, the mobile station begins to monitor the powercontrol bit stream 250 and, in particular, to the power control command252 that is mapped to the particular R-RACH.

Referring now to FIG. 5, there is shown a timing diagram illustratingthe power transmitted by a mobile station on a R-RACH according to thepower control information commands received over the F-PCCH. At thebeginning of the access channel time slot, the mobile station transmitsa preamble portion of the message portion of the access probe at aninitial power level. Typically, the base station must acquire the mobilestation signal and accumulate a series of signal quality indicationsbefore it begins to send power control bits to the mobile station. Thisdelay is shown on both FIGS. 3 and 5 as D3. The remainder of FIG. 5shows an exemplifying sequence of mobile station output powers inresponse to a series of power control commands received from the basestation.

In one embodiment, the power control on the R-RACH is similar to thepower control on the traffic channel as described IS-95. Morespecifically, the base station can compare the power level of thereceived signal to a threshold. If the received signal is below thethreshold, the base station uses the power control information packet tosend a single bit power-up command to the mobile station. Otherwise, thebase station uses the power control information packet to send a singlebit power-down command to the mobile station. In one embodiment, each ofthe power control bits is modulated with BPSK modulation and can,therefore, assume one of three states, namely off, 0 degrees and 180degrees. More information concerning power control can be found in IS-95and in U.S. Pat. Nos. 5,056,109 and 5,265,119, both of which areentitled METHOD AND APPARATUS FOR CONTROLLING TRANSMISSION POWER IN ACDMA CELLULAR TELEPHONE SYSTEM and assigned to the assignee of thepresent invention and incorporated by reference herein in theirentirety.

Such closed loop power control is important for maximizing capacity of amobile radio telephone system according to well known communicationstheories. Closed loop power control permits a mobile station whichbegins a R-RACH access by transmitting its signal with more power thanis needed to be rapidly corrected to the desired power level once thebase station has acquired the mobile station's transmission, thusreducing un-necessary interference in the system. Closed loop powercontrol permits a mobile station which begins a R-RACH access bytransmitting its signal with less power than is needed to be rapidlycorrected to the desired power level once the base station has acquiredthe mobile station's transmission, thus reducing the probability offailure.

The separation of the message portion as well as the provision for powercontrol during transmission of the message portion also lendsflexibility to the system. For example, in a wireless data system, themobile station is likely to generate short bursts of data interspersedbetween significantly longer periods of idleness. Rather thanestablishing a traffic channel each time that the mobile station has aburst of data, it may be advantageous to use the access process justdescribed to bear user data. For example, the message portion of theaccess probe may contain a datagram of bearer traffic.

The invention lends itself particularly well to transmission ofdatagrams for several reasons. According to IS-95A, only a single datarate, 4800 bits/sec, is available for transmission of the access probe.According to the invention, the system can support a variety of datarates during access mode. In general, increased data rates are allowedif the mobile station can increase its transmission power so that theenergy devoted to each bit (E_(b)) remains fairly constant even if theduration of each bit is reduced. For example, in one embodiment, themobile station can increase its data rate to 9600 bit/sec, 19.2kilobits/sec or 38.4 kilobits/sec if sufficient transmission power isavailable. The use of higher data rates allows the mobile station totransfer messages faster than at the lower data rates so that theyconsume the channel for less time and reduce congestion in the system.The use of higher data rates also decreases the time delay associatedwith the transfer of large datagrams. The use of higher data rates ispractical because the closed loop power control which operates on theR-RACH allows the mobile station to increase its transmit power only tothe extent it is necessary.

In addition, the use of a reserved channel allows load control of thesystem. Load control is more intelligent than simple persistence becauseit takes into account the data rate of the incoming signal. If areserved channel carries data at an increased rate, it also consumes amore significant portion of system capacity. In one embodiment, themobile station includes an indication of desired data rate in thepreamble of the request portion. In another embodiment, the mobilestation can include an indication of desired data rate in the preambleof the message portion. In yet another embodiment, the base stationdetermines the data rate by reference to the implicit features of themobile station signals. The base station uses the data rate to determinecurrent system loading. If system loading reaches a predeterminedthreshold, the base station can, for example, begin to send waitmessages to specific or all requesting mobile stations or can directspecific or all mobile stations to use a specified data rate.

In one embodiment of the invention, the system incorporates pseudosofter handoff operation on the forward link, on the reverse link orboth. FIG. 6 is a representational diagram showing the coverage areasectors of a multisectored base station. A multisectored base station270 transmits signals into three different sector coverage areas272A-272C. The sector coverage areas 272A-272C overlap to some extent incoverage overlap areas 274A-274C to provide a continuous coverage areaassociated with the base station. Within the coverage overlap areas274A-274C, the system signal levels are sufficient for the mobilestation to establish bi-directional communication with the base stationthrough the two intersecting sectors. Such operation is detailed in U.S.Pat. No. 5,625,876, entitled METHOD AND APPARATUS FOR PERFORMING HANDOFFBETWEEN SECTORS OF A COMMON BASE STATION, assigned to the assigneehereof and incorporated herein in its entirety by this reference.

FIG. 7 is a block diagram of the multisectored base station 270.Antennas 280A-280C receive signals from sector coverage areas 272A-272C,respectively. In one embodiment, one or more of the antennas 280A-280Care diversity antennas comprising two or more separate antenna elements.The antennas 280A-280C provide received energy to radio frequency (RF)processing blocks 282A-282C, respectively. The RF processing blocks282A-282C down-convert and quantize the received signal energy toproduce digital samples using any one of a myriad of well knowntechniques.

Demodulators 284A-284C receive the digital samples and demodulate one ormore reverse link signals contained therein. In one embodiment, thedemodulators 284A-284C comprise a set of demodulator elements andsearcher elements such as those disclosed in U.S. Pat. No. 5,654,979,entitled CELL SITE DEMODULATION ARCHITECTURE FOR A SPREAD SPECTRUMMULTIPLE ACCESS COMMUNICATION SYSTEMS, assigned to the assignee hereofand incorporated herein in its entirety by this reference. According tothe '979 patent, each demodulator comprises a set of demodulationelements, each of which can be assigned to a multipath propagation ofone of the reverse link signals. The outputs of the demodulationelements are combined to create a resultant signal.

If a mobile station is in softer handoff, two or more of thedemodulators 284 are assigned to demodulate the same reverse linktraffic channel signal from the mobile station. The demodulators 284output demodulated signals to a signal combination block 288 which canfurther merge traffic channel signals received through more than onesector. The output of the signal combination block 288 is coupled to asignal processing unit 290 which performs further signal processing onthe merged output.

A signal generation block 292 creates the forward link signals. Thesignal generation unit 292 provides forward link signals to one or moreof the modulators 286A-286C depending on the location of the mobilestation. Only those sectors with established bi-directionalcommunication transmit a traffic channel to the mobile station, thusreducing interference in those sectors which do not service the mobilestation. The modulators 286A-286C modulate the signals for wireless linktransmission and pass them to the RF processing blocks 282A-282C,respectively. The RF processing blocks 282A-282C convert the digitalbits to analog signals and up-convert them to the desired transmissionfrequency. The antennas 280A-280C radiate the signals into thecorresponding coverage areas sectors 272A-272C.

According to the prior art, the softer handoff techniques are associatedonly with the traffic channel where sustained bi-directionalcommunication is established between the base station and the mobilestation. According to IS-95, the access probes are only received by asingle sector of a multisectored base station regardless of whether themobile station is located in a coverage overlap area. Likewise,according to IS-95, the channel assignment message is transmitted fromonly one sector of a multisectored base station regardless of whetherthe mobile station is located in a coverage overlap area.

In general, each R-CCCH is associated with just one sector and a requestportion of an access probe is detected by only one sector. In oneembodiment of the invention, the base station 270 is configured tobroadcast the F-CACH in all sectors of the base station in a so-calledsimulcast mode. In this way, a mobile station located within a coverageoverlap area transmits the request message 210 to one sector but canreceive the response message 212 from more than one sector, thus,increasing the combined signal energy detected by the mobile station andincrease the probability of successful reception by the mobile station.This type of pseudo softer hand off operation during the access processmimics softer handoff on the forward link traffic channel. Thus, in FIG.7, the signal generation block 292 creates the F-CACH and passes it toeach of the modulators 286A-286C regardless of the origin of the requestportion for which the response messages are generated. These sameprinciples can be applied to transmission of the F-PCCH from multiplesectors. In another embodiment, the reliability of the reception of theF-CACH and F-PCCH by the mobile station is improved within a sector byusing transmit diversity. In this embodiment, replicas of the sameinformation are transmitted on different antenna elements within a givensector, using one or more diversity techniques such as orthogonal codediversity, time division repeated transmission, and delay transmissions.

In a similar manner, this principle can be extended to other basestations operating in the same area. Thus, when a mobile station sends arequest portion of an access probe, a set of base stations in a zonesurrounding the detecting base station respond with transmission of theresponse message. These same principles can be applied to transmissionof the F-PCCH from multiple base stations. This type of pseudo soft handoff operation during the access process mimics soft handoff on theforward link traffic channel.

As noted above, according to IS-95, the base station does not fullydetect the mobile station signal until the entire, rather lengthy,access probe is received the base station. Thus, according to IS-95, thesofter handoff techniques applied to the traffic channel cannot beapplied to the access process because the sector to which the accessprobe is directed cannot identify the signal to the other sectors sothat they may also detect the signal. In contrast, according to theinvention, the majority of the access probe is transmitted over theeasily identifiable R-RACH. Thus, in one embodiment, a plurality ofsectors demodulate the R-RACH and provide corresponding signal energyoutputs. For example, when the request portion 210 is received over aR-CCCH associated with coverage area sector 272A, each of thedemodulators 284-284C attempt to demodulate the R-RACH assigned to themobile station. In this way, if the mobile station is located within oneof the coverage overlap areas 274A-274C, the message portion of theaccess probe is received by each of the corresponding sector'sdemodulators 284. The resultant signals are merged by the signalcommunication block 288 and a single power control indication based uponthe combined signal is generated. As noted above, the power controlindication can be transmitted from more than one sector over a simulcastF-PCCH. This type of pseudo softer hand off operation during the accessprocess mimics softer handoff on the reverse link traffic channel.

In a similar manner, this principle can be extended to other basestations operating in the same area. Thus, when a mobile station sends arequest portion of an access probe, a set of base stations in a zonesurrounding the detecting base station attempt to demodulate the R-RACH.This type of pseudo soft hand off operation during the access processmimics soft handoff on the reverse link traffic channel.

Incorporation of pseudo softer handoff, pseudo soft handoff or both onthe reverse link greatly facilitates the proper operation of the powercontrol on the R-RACH. Unless each base station and sector which iscapable of receiving the mobile station signal at a significant level isable to contribute to the power control commands sent to the mobilestation, the mobile station signal strength can become excessive at thenon-contributing base stations and jam communications therethrough.Therefore, in one embodiment, each surrounding base station and sectorattempts to demodulate the signal from the mobile station on the R-RACHand contributes to the power control command sent to the mobile station.

FIG. 8 is a block diagram of an exemplifying mobile stationarchitecture. An antenna 302 receives and transmits signals over awireless link to a base station. An RF signal processing block 304 iscoupled to the antenna 302. The RF signal processing block 304down-converts and quantizes the received signal energy to producedigital samples using any one of a myriad of well known techniques. TheRF signal processing block 304 is coupled to a modulator/demodulator(modem) 306. The modem 306 receives the quantized energy and demodulatesthe incoming signal under the control of a control 308. In oneembodiment, the modem 306 operates in accordance with U.S. Pat. No.5,764,687, MOBILE DEMODULATOR ARCHITECTURE FOR A SPREAD SPECTRUMMULTIPLE ACCESS COMMUNICATION SYSTEM, which is assigned to the assigneehereof and incorporated herein in its entirety by this reference. Themodem 306 also modulates signals for transmission over the wireless linkunder the control of the controller 308. The modulated signals arecoupled to the RF signal processing block 304 which converts the digitalbits to analog signals and up-converts them to the desired transmissionfrequency for transmission over the antenna 302. In one embodiment, theblocks shown in FIGS. 2A and 2B are carried out by a series ofprocessing units stored in a memory 310 and executed by the controller308. In one embodiment, the mobile station comprises an applicationspecific integrated (ASIC) circuit for execution of the functions. Inanother embodiment, the process blocks are stored in a programmablestorage device.

Although the invention has been described in the context of a CDMAsystem where some of the CDMA channels are further channelized usingtime division techniques, other channelization techniques can benefitfrom the general principles described herein. For example, time divisionmultiple access (TDMA) and frequency division multiple access (FDMA)channels could be used in accordance with the principles of theinvention. In addition, the messages on the channels can be coded andinterleaved. The messages can be repeated and the energies combined toimprove reliability. Quadrature techniques can be used to increase therate at which data is carried over the channels.

Other alternative embodiments will be readily apparent to one skilled inthe art upon examination of the principles discussed herein includingthe simple re-arrangement of the blocks shown in FIGS. 2A and 2B. Forexample, the advantages gained by reducing the size of the mobilestation identification transmitted in the request portion may be gainedby reduction in size in other manners aside from the use of a hashfunction. In one embodiment, the mobile station may randomly choose aquasi-unique identification as a temporary identifier of the mobilestation. In one alternative embodiment, once the mobile station sendsthe request portion of the access probe, it monitors the pilot signalstrength as well as the F-CACH. If the pilot signal strength isrelatively high but the F-CACH does not carry a response message, themobile station determines that the base station did not detect therequest portion because the signal level was too low. Therefore, themobile station, without inserting arbitrary delay, retransmits therequest portion at a higher signal level.

In one embodiment, the base station periodically sends a broadcastaccess control message. The access control message is used by the mobilestation to determine the loading conditions of the system. The accesscontrol message comprises a message type field containing a value whichindicates that the message is an access control message intended forreception by all mobile stations. The access control message alsocomprises a persistence parameter field containing a value which is usedby the mobile station to determine the back-off timer value. The accesscontrol message also comprises a minimum wait time field containing avalue which indicates the minimum value to be used in the persistencetest, for load/flow control. If the minimum wait time field is set toits maximum value, accesses are shut off. Other system configurationinformation and related parameters can be carried on a forward linkcommon control channel such as the paging channel in IS-95.

In another embodiment, the mobile station transmits a pilot sub-channelalong with the message portion of the access probe. The inclusion of thepilot sub-channel may be performed by any one of a myriad of well knowntechniques. The sub-channel can be used by the mobile station to providepower control information to the base station concerning the power levelat which it is receiving the F-PCCH. That is, the mobile station uses asmall fraction of the pilot channel to convey increase or decreasecommands to the base station so that the power allocated to its F-PCCHsub-channel is adjusted to the minimum acceptable level in order toconserve system resources.

In yet another embodiment, if the mobile station has a short message totransfer, it sends a request message on the R-CCCH with the hash ID setto all O's (or some other pre-selected value) which indicates to thebase station that additional data follows immediately and that nochannel assignment is required. The data that follows is transferred,for example, within about 5 msec, and, therefore, is too short torealize any significant benefit from using closed loop power control. Insuch a case, it can be more efficient to communicate this information onthe random access channel rather than wait for the assignment of areserved access channel. The request message is not subject to powercontrol because it is being transmitted on the R-CCCH.

In one embodiment, the channel assignment message has a 1 bit indicationwhich is used to inform the accessing mobile station that the basestation has received multiple request portion messages in the sameaccess slot. In this way, a mobile station awaiting a response on theF-CACH more quickly determines whether it should resend the requestportion at a higher power level or the same power level or continue towait for an assignment message. This feature can be used to reducetransmission delay.

In another embodiment, the channel assignment message may contain apower control correction value which is used by the mobile station toadjust its transmit power prior to closed loop power control beingenabled on the reserved channel. In this scheme, the base stationdetermines the adjustment necessary to support reliable communicationsbased on, for example, the requested or assigned data rate as well asthe received energy detected over the request portion of the mobilestation's transmission.

In still a further embodiment, a class wait message is used to effectthe behavior of a class of mobile stations attempting to access thesystem. A class wait message indicates that those mobile stations whichhave a class mark less than or equal to a class mark threshold areforced to use a different set of persistence and back-off parameters orto cease attempting to access the system and revert back to monitoringthe appropriate overhead channel to get updated access parameters. Thosemobile stations which have a class mark greater than the class markthreshold are permitted to continue accessing the system, either usingexisting or updated persistence and back-off parameters. In this way,the system has a mechanism for quickly disabling accesses in aprioritized manner in order to control loading.

In yet another embodiment, mobile stations wishing to access the systemcan monitor the activity on the F-PCCH, F-CACH or both in order toderive an estimate of system loading. This estimate can be used toaffect the parameters that affect the access behavior of the mobilestation, such as persistence, back-off, data rate, and such. This schemecan be used effectively to increase the efficiency of the requestchannel in certain operating environments.

In one embodiment, the invention is embodied in a system which uses aset of binary code sequences as signatures. For example, the preamblesent by the mobile station to the base station to access the system isone of a set of predetermined, distinguishable code sequences calledsignatures. The mobile station selects one of the signatures to transmiteach time it attempts to access the system. For example, the mobilestation randomly selects one of 16 different 1 msec long signatures andtransmits it during one of a series of 1.25 msec time slots. Or, themobile station can generate a signature based upon the mobile station'suniquely identifying number.

The base station monitors the R-CCCH for each of the 16 signatures inall time slots. When the base station detects a signature, it respondsto the mobile station on the F-CACH with a message which reflects thesignature used by the mobile station. For example, in one embodiment,the base station responds to the mobile station on the F-CACH using amessage modulated with the same binary code sequence used by the mobilestation. In another embodiment, the base station responds with a messagemodulated by a different binary code sequence which is associated withthe signature used by the mobile station in a predetermined fashion. Inanother embodiment, the base station responds on the F-CACH by includinga field which designates the signature used by the mobile station. Forexample, if there are 16 signatures available, the base station canspecify which signature of the access probe to which it is responding bya field with four bits. In this way, the overhead burden of atransmitting the hash function is eliminated on both the F-CACH and theR-CCCH, thus decreasing the amount of system resources expended on thesetasks.

In one embodiment, each signature comprises a 256 bit sequence which isrepeated 16 times and which is modulated according to 16 bit mask. Onthe reverse link, the sequence can be a segment of a Gold code such asthose describe on pages 833 and 834 of John Proakis, DigitalCommunications, Second Edition, McGraw-Hill Book Company (1989). On theforward link, the sequence can be an orthogonal variable spreadingfactor (OVSF) code or variable length or hierachical Walsh code oflength 256 as are well known in the art. In this way, the forward linktransmission on the F-CACH are orthogonal to the other forward linktransmissions.

In one embodiment, one or more of the binary code sequences used by thebase station on the F-CACH are reserved to indicate a level of loadingat the base station. For example, one of the binary code sequences canindicate that a maximum loading has been exceed, thus indicating to themobile station to wait until the load indicator is turned off, to entera back-off procedure according to persistence parameters or both. Inthis embodiment, after transmitting a signature over the R-CCCH, themobile station monitors the F-CACH in order to detect the responsivemessage corresponding to the transmitted signature as well as one ormore of the signatures which indicate the level of loading.

In one embodiment, the polarity of the binary code sequence transmittedby the base station on the F-CACH conveys information to the mobilestation. For example, the polarity of the code sequence can be used toconvey power control information to the mobile station. One polarity canindicate to the mobile station to increase the level at which ittransmits on the R-RACH above the level used on the R-CCCH and theinverse polarity can indicate to the mobile station to decrease thelevel at which it transmits on the R-RACH below the level used on theR-CCCH. The polarity could also be used to set or limit the data rate atwhich the mobile station transmits on the R-RACH.

The use of signatures can be characterized as the use of a limitednumber of semi-unique ID's (such as the hash ID's) used to modulate thesignal. In one embodiment, a randomly chosen signature is modulatedaccording to a hash ID associated with the mobile station. In anotherembodiment, the hash ID is carried as data in a message modulated withthe signature. When the base station responds on the F-CACH, theresponse message can indicate the hash ID. The use of a hash ID reducesthe probability of false capture if two mobile stations use the samesignature at the same time but the base station detects only one. If themobile station whose signal was not detected decodes the message on theR-RACH comprising the hash ID of the other mobile station, it can thusdetermine that the R-RACH transmission is intended for another mobilestation.

In one embodiment, the hash ID is transferred implicitly over theF-CACH. For example, the binary code sequence used to modulate thechannel assignment message is a unique function of the hash ID. Thus,the hash ID is not sent explicitly along with the other data intendedfor the mobile, but instead is used to select or modify the code used onthe F-CACH. The mobile station demodulates the F-CACH using the codesequence derived based on its own hash ID and, if it successfullydecodes the acknowledgement, can proceed to transmit the remainder ofthe message on the assigned R-RACH channel. In one embodiment, aseparate forward link channel which is orthogonal to all other forwardlink channels is used to convey the hash ID and other data. In anotherembodiment, the hash ID is used to modify the existing sequence used onthe forward link channel used to convey the hash ID and other data. Inthis way, the binary code sequence used on the F-CACH can be function ofthe signature, the hash ID or both.

The invention may be embodied in other specific forms without departingfrom its spirit or essential characteristics. The described embodimentis to be considered in all respects only as illustrative and notrestrictive and the scope of the invention is, therefore, indicated bythe appended claims rather than the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. In a communication system, a method of accessinga base station from a mobile station, comprising: selecting a firstsignature sequence from a plurality of signature sequences used bymultiple mobile stations; transmitting a request portion of an accessprobe over a reverse link common control channel subject to contention,said access probe modulated with said signature sequence; receiving achannel assignment message from said base station designating a reservedaccess channel, said reserved access channel providing communicationwith a low probability of contention and said channel assignment messagereflecting said first signature; transmitting a message portion of saidaccess probe over said reserved access channel, wherein saidtransmitting said message portion facilitates reception of said messageportion by a plurality of base stations; receiving a power controlcommand over a forward link channel associated with said reserved accesschannel; and responding to said power control command by increasing ordecreasing a power level at which said mobile station transmits saidmessage portion.
 2. The method of claim 1, wherein said message portioncomprises an overhead message.
 3. The method of claim 1, wherein saidmessage portion comprises user data.
 4. The method of claim 1, whereinsaid transmitting said message portion occurs at one of a plurality ofavailable data rates.
 5. In a communication system, a method ofaccessing a base station from a mobile station, comprising: selecting afirst signature sequence from a plurality of signature sequences used bymultiple mobile stations; transmitting a request portion of an accessprobe over a reverse link common control channel subject to contention,said access probe modulated with said signature sequence; receiving achannel assignment message from said base station designating a reservedaccess channel, said reserved access channel providing communicationwith a low probability of contention and said channel assignment messagereflecting said first signature; transmitting a message portion of saidaccess probe over said reserved access channel, wherein said messageportion comprises a call origination message; receiving a power controlcommand over a forward link channel associated with said reserved accesschannel; and responding to said power control command by increasing ordecreasing a power level at which said mobile station transmits saidmessage portion.
 6. In a communication system, a method of accessing abase station from a mobile station, comprising: selecting a firstsignature sequence from a plurality of signature sequences used bymultiple mobile stations; transmitting a request portion of an accessprobe over a reverse link common control channel subject to contention,said access probe modulated with said signature sequence; receiving achannel assignment message from said base station designating a reservedaccess channel, said reserved access channel providing communicationwith a low probability of contention and said channel assignment messagereflecting said first signature; transmitting a message portion of saidaccess probe over said reserved access channel, wherein said messageportion is longer than said request portion; receiving a power controlcommand over a forward link channel associated with said reserved accesschannel; and responding to said power control command by increasing ordecreasing a power level at which said mobile station transmits saidmessage portion.
 7. The method of claim 1, wherein said request portioncomprises an identification which quasi-uniquely identifies said mobilestation.
 8. The method of claim 7, further comprising determining saididentification which quasi-uniquely identifies said mobile station froma unique identifying number associated with said mobile station using ahash function.
 9. The method of claim 7, further comprising randomlyselecting said identification which quasi-uniquely identifies saidmobile station.
 10. In a communication system, a method of accessing abase station from a mobile station, comprising: selecting a firstsignature sequence from a plurality of signature sequences used bymultiple mobile stations; transmitting a request portion of an accessprobe over a reverse link common control channel subject to contention,said access probe modulated with said signature sequence; receiving achannel assignment message from said base station designating a reservedaccess channel, said reserved access channel providing communicationwith a low probability of contention and said channel assignment messagereflecting said first signature and specifying a wait period to beobserved; transmitting a message portion of said access probe over saidreserved access channel; receiving a power control command over aforward link channel associated with said reserved access channel;responding to said power control command by increasing or decreasing apower level at which said mobile station transmits said message portion;and delaying said transmitting said message portion with reference tosaid wait period.
 11. In a communication system, a method of accessing abase station from a mobile station, comprising: selecting a firstsignature sequence from a plurality of signature sequences used bymultiple mobile stations; transmitting a request portion of an accessprobe over a reverse link common control channel subject to contention,said access probe modulated with said signature sequence; receiving achannel assignment message from said base station designating a reservedaccess channel, said reserved access channel providing communicationwith a low probability of contention and said channel assignment messagereflecting said first signature and specifying a power controlinformation; transmitting a message portion of said access probe oversaid reserved access channel; receiving a power control command over aforward link channel associated with said reserved access channel; andresponding to said power control command by increasing or decreasing apower level at which said mobile station transmits said message portion;and determining a power level at which to transmit said message portionwith reference to said power control information.
 12. The method ofclaim 11, wherein said channel assignment message is spread with asecond spreading sequence, said second spreading sequence reflectingsaid first signature.
 13. The method of claim 12, wherein a polarity ofsaid second spreading sequence conveys mobile station information. 14.The method of claim 13, wherein said mobile station information is powercontrol information.
 15. The method of claim 13, wherein said mobilestation information is data rate information.
 16. The method of claim 1,wherein said forward link channel is expressly specified in said channelassignment message.
 17. In a communication system, a method of accessinga base station from a mobile station, comprising: selecting a firstsignature sequence from a plurality of signature sequences used bymultiple mobile stations; transmitting a request portion of an accessprobe over a reverse link common control channel subject to contention,said access probe modulated with said signature sequence; receiving achannel assignment message from said base station designating a reservedaccess channel, said reserved access channel providing communicationwith a low probability of contention and said channel assignment messagereflecting said first signature; transmitting a message portion of saidaccess probe over said reserved access channel; receiving a powercontrol command over a forward link channel associated with saidreserved access channel; and responding to said power control command byincreasing or decreasing a power level at which said mobile stationtransmits said message portion; receiving a message from said basestation modulated with a predetermined sequence, said predeterminedsequence reflecting a level of loading at said base station.
 18. Amobile communication station, comprising: a controller configured togenerate a first signature sequence from a plurality of signaturesequences used by multiple mobile stations; a modulator coupled to saidcontroller, said modulator being configured to modulate a requestportion of an access probe with said first signature sequence and tomodulate a message portion of said access probe; a radio frequencysignal processing unit coupled to said modulator, said signal processingunit being configured to transmit said request portion over a forwardlink common control channel subject to contention and configured toreceive a channel assignment message reflecting said first signature anda reserved access channel, said reserved access channel providingcommunication with a low probability of contention and configured totransmit said modulated message portion over said reserved accesschannel, said radio frequency signal processing unit comprising: a powercontrol apparatus configured to receive a power control command over aforward link channel and configured to respond thereto by increasing ordecreasing a power level at which said mobile station transmits saidmessage portion; and a demodulator coupled to said radio frequencysignal processing unit and said controller, said demodulator configuredto demodulate said channel assignment message according to a secondsignature sequence associated with said first signature sequence.
 19. Amobile communication station, comprising: a controller configured togenerate a first signature sequence from a plurality of signaturesequences used by multiple mobile stations; a modulator coupled to saidcontroller, said modulator being configured to modulate a requestportion of an access probe with said first signature sequence and tomodulate a message portion of said access probe; a radio frequencysignal processing unit coupled to said modulator, said signal processingunit being configured to transmit said request portion over a forwardlink common control channel subject to contention and configured toreceive a channel assignment message reflecting said first signature anda reserved access channel, said reserved access channel providingcommunication with a low probability of contention and configured totransmit said modulated message portion over said reserved accesschannel, said radio frequency signal processing unit comprising: a powercontrol apparatus configured to receive a power control command over aforward link channel and configured to respond thereto by increasing ordecreasing a power level at which said mobile station transmits saidmessage portion, wherein said radio frequency signal processing unit isfurther configured to receive said power control command from aplurality of sectors associated with a single base station; and ademodulator coupled to said radio frequency signal processing unit andsaid controller, said demodulator configured to demodulate said channelassignment message.
 20. A method of communication system access,comprising: receiving a request portion of an access probe modulatedwith a first signature sequence selected from among a plurality ofsignature sequences which provide communication subject to contention;transmitting a channel assignment message designating said firstsignature sequence and a reserved access channel, said reserved accesschannel providing communication with a low probability of contention;receiving a message portion of said access probe over said reservedaccess channel from a mobile station, wherein said channel assignmentmessage specifies a wait period to be observed before said receivingsaid message portion is executed; and transmitting a power controlcommand over a forward link channel based upon a signal quality level atwhich said message portion is received during said receiving saidmessage portion.
 21. The method of claim 20, wherein said step ofreceiving said message portion is performed by a plurality of sectorsassociated with a base station.
 22. The method of claim 20, wherein saidrequest portion comprises an identification which quasi-uniquelyidentifies said mobile station.
 23. A method of communication systemaccess, comprising: receiving a request portion of an access probemodulated with a first signature sequence selected from among aplurality of signature sequences which provide communication subject tocontention; transmitting a channel assignment message designating saidfirst signature sequence and a reserved access channel, said reservedaccess channel providing communication with a low probability ofcontention; receiving a message portion of said access probe over saidreserved access channel from a mobile station; and transmitting a powercontrol command over a forward link channel based upon a signal qualitylevel at which said message portion is received during said receivingsaid message portion; determining a power correction amount based upon asignal quality level at which said request portion is received andwherein said channel assignment message specifies said power controlcorrection amount to be used by said mobile station to transmit saidmessage portion.
 24. The method of claim 23, further comprising the stepof transmitting a power control command through a plurality of sectorsassociated with said base station, said transmitting step beingperformed in response to a signal quality level at which said messageportion is received.
 25. A method of communication system access,comprising: receiving a request portion of an access probe modulatedwith a first signature sequence selected from among a plurality ofsignature sequences which provide communication subject to contention;transmitting a channel assignment message designating said firstsignature sequence and a reserved access channel, said reserved accesschannel providing communication with a low probability of contention,and wherein said transmitting said channel assignment message includesmodulating said channel assignment message with a second signaturesequence, said second signature sequence associated with said firstsignature sequence; receiving a message portion of said access probeover said reserved access channel from a mobile station; andtransmitting a power control command over a forward link channel basedupon a signal quality level at which said message portion is receivedduring said receiving said message portion.
 26. A method ofcommunication system access, comprising: receiving a request portion ofan access probe modulated with a first signature sequence selected fromamong a plurality of signature sequences which provide communicationsubject to contention; transmitting a channel assignment messagedesignating said first signature sequence and a reserved access channel,said reserved access channel providing communication with a lowprobability of contention; receiving a message portion of said accessprobe over said reserved access channel from a mobile station;transmitting a power control command over a forward link channel basedupon a signal quality level at which said message portion is receivedduring said receiving said message portion; and transmitting a loadingmessage modulated with a spreading sequence which reflects a level ofloading at a base station.